Building a Tree from DataTable results with the node structure formatted as \Node1\Node2\

Hi,
I've been banging my head against a wall for the past few days with the problem of turning DataTable results into a Tree Structure to populate a TreeView control. The tree path is stored in a field called Path.

Normally I do a recursive query using parent ID's but this system is different as the Root Parents Childs are all stored in the string. I've been doing a For each Row in DataSet and breaking down each Path into a string array using NodeList = Path.Split(CChar("\")) but its the building of the nodes that I just cant get my head around.

Idealy I dont want to requery the database again, the results in the datatable from a stored procedure with a fair few params. So I'd have to work with data just in the datatable.

Though I think the toughest problem isnt the recursive part its working with the path.

Here is the code I've done so far. it almost works but I cant work out why it gets stuck in a loop.

Tracing through it would make the following nodes

D
D\1
D\1\A
D\1\A\1
D\1\A\2
D\1\A\3
D\1\A\4

then it would start again back at D\1\A point and loop forever.

LocationTreeView.Nodes.Clear()
For Each root As String In GetNodeRoots(locationList)
LocationTreeView.Nodes.Add(BuildNode(root, locationList))
Next
Public Function GetNodeRoots(ByRef list As DataTable) As Collection
Dim rootNodes As New Collection
Dim lastRoot As String = String.Empty
For Each row As DataRow In list.Rows
Dim nodeList() As String = row("LocationName").ToString.Split(CChar("\"))
If lastRoot <> nodeList(0) Then
rootNodes.Add(nodeList(0))
lastRoot = nodeList(0)
End If
Next
Return rootNodes
End Function
Public Function BuildNode(ByVal path As String, ByRef list As DataTable) As TreeNode
' Get the current path where we are upto.
Dim currentPath() As String = path.Split(CChar("\"))
' Create next node.
Dim node As New TreeNode(currentPath(currentPath.GetUpperBound(0)))
' Get a filtered list of all the child nodes for the path passed in.
For Each row As DataRow In list.Select(String.Concat("LocationName LIKE '", String.Concat(path, "\"), "%'"))
' Get the full path of the next node.
Dim nextNode() As String = row("LocationName").ToString.Split(CChar("\"))
' If the next node has any more childs then call the recursive function.
If nextNode.Count > currentPath.Count Then
' Make the next path we pass in just 1 step along from the current path.
ReDim Preserve nextNode(currentPath.Count)
' Call recursive funxtion with the new path, rejoin the path back to its orginal format also.
node.Nodes.Add(BuildNode(String.Join("\", nextNode), list))
End If
Next
Return node
End Function

Ok while some essential tweeks to the above code for efficency I stumbled accross the probem,

the problem lies with that line

For Each row As DataRow In list.Select(String.Concat("LocationName LIKE '", path, "\", "%'"))

It works fine except for its returning to much, if the [path] was

LocationName LIKE 'A\1\%'

it works but its returning multipule entries due to there been no GROUP BY or SELECT DISTINCT clauses.
The problem is I only know how to filter the results in DataTable.Select with parameters. Can you do this in the DataTable or do I have to resort to doing it manually in the code itself?

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tbh pretty much the same I just changed how I was building strings, I had some extra steps in there that wasn't needed, which since this would be looping several 1000's times (alot of records in the DataTable) I didnt want to many overheads.

Looking at whats happening or what we want to stop happening. The Select clause is ment to retrive a list of the Childs ware are to build nodes for then pass those Childpaths into the function again but if them childs have subChilds we have duplicate requests. So we need to remove them duplicates since were not intrested in them.

I can only think of 2 ways atm, either Create a function that filders the orginal Array of DataRows() removing all duplicates before we start the for next loop. or do an extra check and verify the previously processed node is not = to the next node were about to process. ?? /shrug :)

Tried both methods and the overheads are to high takes 5-6Ssecs pn my PC to generate 1011 nodes.
Which is far to long as the final plan would be much larger. The problem is working with the DataTable only. So I'll write it so I can actually query the database for the child nodes and let the database do the filtering.

foreach row in the DataTable
string() nodes = locationName.ToString().Split("\")
use the nodes array to traverse down the treeview nodes to find node
if node is not created yet
create node (any additional details for the node must be updated later)
else
update node information, if anything needs to be updated
end of treeview traversal
end of foreach

The idea is instead of going by the tree structure and search for its child-node from the DataTable, we loop by the DataTable and create the node immediately (including its ancestor nodes, if they aren't created yet).

I believe the 1st method has O(n^2) complexity, because there are n items in the tree, and each search for a node's children in the DataTable requires us to roughly traverse almost all n items.

While the 2nd method should be a little better O(n log n). Because we only need to traverse the whole table once, that is O(n). And for each item, we search for its location in the tree, which is roughly O(log n). Theoretically, this should be faster, and no duplicates too :) and it does not need recursion ...

Unfortunately, I'm tied down with my office work at the moment, couldn't test it out myself. You can try it out if you want to...

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